Abstract 056 (late submission)
120+ µA Single 18F- Target and Beam Port Upgrade for the RDS/Eclipse
Matthew H. Stokely1, Thomas M. Stewart2 and Bruce W. Wieland1
1
Bruce Technologies, Inc., Chapel Hill, NC, USA, 27514
D-Pace, Inc., PO Box 201, Nelson, BC, Canada, V1L 5P9
2
A high power (>1.3 kW) target platform has been developed for the RDS-111/Eclipse
and RDS-112 cyclotrons. This fully engineered solution includes upgrades to four subsystems:
target, beam port, target support unit and deionized water cooling system. This platform has been
in service 6 days per week since August 2009. The target is operated within an intensity range of
100 to 120 µA with a mean 18F saturation yield of 121 mCi/µA. Only 2300 µL of [18O]enriched water
is consumed each irradiation, resulting in one of the highest aqueous 18F target power densities to
date (570 W/cc). In addition to offering unprecedented performance, the single target platform
greatly simplifies operation and improves the overall robustness of the cyclotron system.
The water target model CF-1000 is a conventionally pressurized cousin to the highly
optimized, bottom pressurized Thermosyphon target. Due to the small volume of the target and the
simplicity of using the OEM target support unit software, bottom pressurization was not viable. The
target insert is constructed of either EB melted or arc cast tantalum or niobium, and is housed in a
6061 aluminum body. The conduction layer between cooling water and target medium is less than
0.030” for all chamber surfaces except the target window, and the flow regime is fully developed
turbulent in all cooling water passages. To achieve turbulent conditions a conservative minimum
flow rate of 2.5 GPM is required for this specific geometry. Window cooling is provided by nucleate
boiling in the target medium.
The single target port replaces the rotating “turret” target changer on the 111/Eclipse
cyclotron. The port includes a beam tube, vacuum isolation valve, water cooled graphite collimator,
and vacuum roughing line. The assembly is constructed primarily of hard anodized 6061 aluminum
for ruggedness and electrical isolation.
Some PEEK is used sparingly in high
wear areas and critical insulating
layers. The ring collimator is made of
very low porosity ATJ grade graphite to
mitigate water absorption during target
changes.
This
greatly
shortens
subsequent pump down time. The
graphite is baked out at 150C under 10
microns partial vacuum prior to
installation. The assembly mounts to
the cyclotron steel via the carrier plate
which
allows
for
independent
adjustment in x and y via small lead
screws. The collimator, port and beam
tube section interface with the carrier
plate via a spherical bearing, which is
Figure 1: CF-1000 Installed on RDS-111 Cyclotron
clamped in place after alignment
adjustments are made. This ensures that the collimator and target are coaxial at all times and
provides an extremely rigid yet easily adjustable mount.
A larger recirculation pump is installed in the water system to accommodate the
additional flow requirements. To ensure that proper flow balance is maintained, adjustable
distribution manifolds are installed at the recirculation pump inlet and outlet. The supply manifold
has a back-pressure regulating valve to allow bypass flow. This prevents both dead heading and
overpressure conditions when the cyclotron is shut down. The upgrades to the water system are a
small fraction of the total system fabrication cost and critical to high performance operation.
The target support unit(TSU) geometry was redesigned to mitigate the pressure rise
from elevated vapour fraction at high intensity and to improve liquid recovery. The OEM software is
used to operate the TSU so the functionality remained the same. Significant improvement is made
from a maintenance perspective as a much more suitable pressure transducer is used resulting in
smaller hysteresis, increased robustness and a reduction in replacement cost of more than a factor
of five.
The performance history of the target system is shown in figure 2. The product was
used exclusively for clinical 18FDG, and showed radiochemical yields consistently within
specifications for both synthesis modules used. Note that the discontinuity at run number 65 is
due to change in the Capintec CRC-15PET dose calibrator settings. This is the result of a
technical bulletin issued by Capintec in 2009.
Saturation Yield Performance (26 Weeks)
160
150
140
Saturation Yield (mCi/µA)
130
120
110
100
90
80
70
60
0
20
40
60
80
100
120
140
160
Run Number (dimensionless)
Figure 2: Operational Performance from DV3
180
200